1. Field of the Invention
The present invention relates to a digital recorder capable of digitally recording, reproducing or editing, a digital signal such as an audio signal (voice signal) and a video signal.
2. Description of the Related Art
Conventionally, as a method of recording, reproducing and editing an audio signal, an analog audio signal is recorded on a magnetic tape, and the recorded signal is reproduced or edited. Since this prior art involves analog recording/reproduction, deterioration of the sound quality is inevitable. Particularly, the deterioration will be prominent when the once-recorded audio signal is dubbed.
Further, the use of the magnetic tape as a recording medium raises problems such that it takes time to reach the target editing point, and edition requires that the target recorded portion of the magnetic tape be physically cut and pasted or be copied to somewhere else before actually executing the edition.
The problem about the deterioration of the sound quality can be overcome by employing a method of digitally recording data on a magnetic tape. However, there still remains a shortcoming concerning the freedom of locating the starting point or edition due to the use of a sequential-access type recording medium.
There has been proposed a solution to the conventional problems which uses a Winchester type hard disk as a recording medium (refer to, for example, JAS Journal '89, April, pages 16 to 22, "Trend of Digital Audio Workstation (DAW)--January Session in AES Japan").
In general, an external memory device, such as a hard disk or an opto-electromagnetic disk, has a lower data transfer rate than RAM, requiring more accessing time. This is a bottleneck particularly in executing data recording/reproduction over multiple tracks in real time in a single external memory device.
In the case of reproducing edited audio data acquired by performing some edition, such as insertion or deletion of desired data, on the audio data read from an external memory device, it is necessary to provide so-called cross fade of a signal with a length of 3 ms to 30 ms before and after an editing point in order to prevent an unnatural sound or data discontinuity. Two conventional methods to realize the cross fade are:
(1) The first method is to rewrite audio data recorded on a hard disk itself. This method makes it difficult to correct the audio data, and does not make the best use of the random accessible feature of data that is recorded on the hard disk.
(2) The second method is real-time processing such that a central processing unit (CPU) stores information about the editing point of audio data recorded on a hard disk, without rewriting the data itself, controls access to the hard disk to read out two data blocks before and after the editing point, and prepares a single data block for the interval of the cross fade. This method would be the best choice in light of the convenience of edition. However, this method requires accessing two tracks for handling the amount of data corresponding to a signal track. In performing the cross-fade process on all of the tracks at the same editing point, however, it is necessary to provide for data transfer width (data transfer rate, of) twice the number of tracks. Further, real-time cross-fade processing needs high-speed signal processing. Therefore, a high-cost device is needed to realize the second method.
In the conventional apparatus, only audio data and sequencer data (MIDI data) are recorded/reproduced by special purpose recorders. Although attempts have been made to integrate these data and video data to record/reproduce them and to integrate and edit these data, only unsatisfactory results have been obtained so far.